Are you absolutely sure the head gasket is blown. Its a big job to tackle but if you feel proficient, and have the necessary tools you will need proper information.
You can buy a workshop manual, most of which are a little to generic.
There is a service that allows you access to Nissan workshop manual information, technical service bulletins for your truck and more that is cheap, easy to navigate and professional level information.
http://www.alldatadiy.com/